Radiation hydrodynamic simulations of super-Eddington accretion flows

2006 ◽  
Vol 2 (S238) ◽  
pp. 301-304
Author(s):  
Ken Ohsuga
Keyword(s):  
Accretion Rate ◽  
Radiation Force ◽  
Critical Value ◽  
Hydrodynamic Simulations ◽  
Mass Accretion Rate ◽  
Accretion Flows ◽  
Supercritical Accretion ◽  
Outflow Region ◽  
Photon Trapping ◽  
Disk Region

AbstractWe perform the two-dimensional radiation-hydrodynamic simulations to study the radiation pressure-dominated accretion flows around a black hole (BH). Our simulations show that the highly supercritical accretion flow (mass accretion rate is much larger than the critical value) is composed of the disk region and the outflow region above the disk.The radiation force supports the thick disk and drives the outflow. The photon trapping plays an important role within the disk, reducing the disk luminosity. On the other hand, in the case that mass accretion rate moderately exceeds the critical value, we find that the disk is unstable and exhibits the limit-cycle oscillations. The disk oscillations in our simulations nicely fit to the variation amplitude and duration of quasi-periodic luminosity variations observed in the GRS 1915+105 microquasar.

scholarly journals Hydrodynamics of Accretion Columns

1987 ◽  
Vol 93 ◽  
pp. 591-594
Author(s):  
H. Herold ◽  
K. Wolf ◽  
H. Ruder
Keyword(s):  
Accretion Rate ◽  
Radiation Transport ◽  
Critical Value ◽  
Stationary Solutions ◽  
Time Dependent ◽  
Physical Parameters ◽  
High Luminosity ◽  
Accretion Flows ◽  
Accretion Rates ◽  
Parameter Ranges

AbstractA detailed understanding of how the infalling matter in accretion columns is decelerated is essential for the calculation of the emitted radiation. On neutron stars, the deceleration takes place mainly by the interaction of the plasma with radiation, at least for the high-luminosity sources. We report on our two-dimensional calculations of the hydrodynamic flow in such accretion columns. The radiation transport is treated in the diffusion approximation, and we are looking for a stationary solution for the velocity field. The dependence of the results on physical parameters, especially on the accretion rate is discussed. Due to the non-linearity of the problem it turns out that only in certain parameter ranges stationary solutions seem to exist. For accretion rates higher than a critical value there are no stationary accretion flows. This leads us to the conclusion that a time-dependent picture for the accretion is unavoidable.

scholarly journals Choked accretion: from radial infall to bipolar outflows by breaking spherical symmetry

2019 ◽  
Vol 490 (4) ◽  
pp. 5078-5087 ◽  
Author(s):  
Alejandro Aguayo-Ortiz ◽  
Emilio Tejeda ◽  
X Hernandez
Keyword(s):  
Steady State ◽  
Spherical Symmetry ◽  
Large Scale ◽  
Accretion Rate ◽  
Polar Regions ◽  
Bipolar Outflows ◽  
Accretion Flows ◽  
A Value ◽  
Outflow Region ◽  
Steady State Solutions

ABSTRACT Steady-state, spherically symmetric accretion flows are well understood in terms of the Bondi solution. Spherical symmetry, however, is necessarily an idealized approximation to reality. Here we explore the consequences of deviations away from spherical symmetry, first through a simple analytic model to motivate the physical processes involved, and then through hydrodynamical, numerical simulations of an ideal fluid accreting on to a Newtonian gravitating object. Specifically, we consider axisymmetric, large-scale, small-amplitude deviations in the density field such that the equatorial plane is overdense as compared to the polar regions. We find that the resulting polar density gradient dramatically alters the Bondi result and gives rise to steady-state solutions presenting bipolar outflows. As the density contrast increases, more and more material is ejected from the system, attaining speeds larger than the local escape velocities for even modest density contrasts. Interestingly, interior to the outflow region, the flow tends locally towards the Bondi solution, with a resulting total mass accretion rate through the inner boundary choking at a value very close to the corresponding Bondi one. Thus, the numerical experiments performed suggest the appearance of a maximum achievable accretion rate, with any extra material being ejected, even for very small departures from spherical symmetry.

scholarly journals The splashback boundary of haloes in hydrodynamic simulations

2021 ◽  
Author(s):  
Stephanie O’Neil ◽  
David J Barnes ◽  
Mark Vogelsberger ◽  
Benedikt Diemer
Keyword(s):  
Dark Matter ◽  
Density Profile ◽  
Accretion Rate ◽  
Radial Density ◽  
Density Profiles ◽  
Hydrodynamic Simulations ◽  
Mass Accretion Rate ◽  
Significant Difference ◽  
Satellite Galaxies

Abstract The splashback radius, Rsp, is a physically motivated halo boundary that separates infalling and collapsed matter of haloes. We study Rsp in the hydrodynamic and dark matter only IllustrisTNG simulations. The most commonly adopted signature of Rsp is the radius at which the radial density profiles are steepest. Therefore, we explicitly optimise our density profile fit to the profile slope and find that this leads to a $\sim 5\%$ larger radius compared to other optimisations. We calculate Rsp for haloes with masses between 1013 − 15M⊙ as a function of halo mass, accretion rate and redshift. Rsp decreases with mass and with redshift for haloes of similar M200m in agreement with previous work. We also find that Rsp/R200m decreases with halo accretion rate. We apply our analysis to dark matter, gas and satellite galaxies associated with haloes to investigate the observational potential of Rsp. The radius of steepest slope in gas profiles is consistently smaller than the value calculated from dark matter profiles. The steepest slope in galaxy profiles, which are often used in observations, tends to agree with dark matter profiles but is lower for less massive haloes. We compare Rsp in hydrodynamic and N-body dark matter only simulations and do not find a significant difference caused by the addition of baryonic physics. Thus, results from dark matter only simulations should be applicable to realistic haloes.

scholarly journals Searching for super-Eddington quasars using a photon trapping accretion disc model

2020 ◽  
Vol 492 (3) ◽  
pp. 4058-4079
Author(s):  
Quentin Pognan ◽  
Benny Trakhtenbrot ◽  
Tullia Sbarrato ◽  
Kevin Schawinski ◽  
Caroline Bertemes
Keyword(s):  
Selection Criteria ◽  
Accretion Rate ◽  
Accretion Disc ◽  
Spectral Energy ◽  
Wide Field ◽  
Field Surveys ◽  
Accretion Flows ◽  
Wide Range ◽  
Photon Trapping ◽  
Formation And Evolution

ABSTRACT Accretion on to black holes at rates above the Eddington limit has long been discussed in the context of supermassive black hole (SMBH) formation and evolution, providing a possible explanation for the presence of massive quasars at high redshifts (z ≳ 7), as well as having implications for SMBH growth at later epochs. However, it is currently unclear whether such ‘super-Eddington’ accretion occurs in SMBHs at all, how common it is, or whether every SMBH may experience it. In this work, we investigate the observational consequences of a simplistic model for super-Eddington accretion flows – an optically thick, geometrically thin accretion disc where the inner-most parts experience severe photon-trapping, which is enhanced with increased accretion rate. The resulting spectral energy distributions (SEDs) show a dramatic lack of rest-frame UV, or even optical, photons. Using a grid of model SEDs spanning a wide range in parameter space (including SMBH mass and accretion rate), we find that large optical quasar surveys (such as SDSS) may be missing most of these luminous systems. We then propose a set of colour selection criteria across optical and infrared colour spaces designed to select super-Eddington SEDs in both wide-field surveys (e.g. using SDSS, 2MASS, and WISE) and deep and narrow-field surveys (e.g. COSMOS). The proposed selection criteria are a necessary first step in establishing the relevance of advection-affected super-Eddington accretion on to SMBHs at early cosmic epochs.

scholarly journals The relativistic mass accretion rate for accretion disk in the equatorial of rapidly rotating neutron stars

2021 ◽  
Vol 1869 (1) ◽  
pp. 012156
Author(s):  
A Yasrina ◽  
N Widianingrum ◽  
N S Risdianto ◽  
D Andra ◽  
N A Pramono ◽  
...  
Keyword(s):  
Neutron Stars ◽  
Accretion Disk ◽  
Accretion Rate ◽  
Mass Accretion Rate ◽  
Relativistic Mass

scholarly journals TWO-DIMENSIONAL NUMERICAL SIMULATIONS OF SUPERCRITICAL ACCRETION FLOWS REVISITED

2013 ◽  
Vol 780 (1) ◽  
pp. 79 ◽  
Author(s):  
Xiao-Hong Yang ◽  
Feng Yuan ◽  
Ken Ohsuga ◽  
De-Fu Bu
Keyword(s):  
Numerical Simulations ◽  
Two Dimensional ◽  
Accretion Flows ◽  
Supercritical Accretion

scholarly journals Searching for a link between the magnetic nature and other observed properties of Herbig Ae/Be stars

2008 ◽  
Vol 4 (S259) ◽  
pp. 395-396 ◽  
Author(s):  
Swetlana Hubrig ◽  
C. Grady ◽  
M. Schöller ◽  
O. Schütz ◽  
B. Stelzer ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Survey ◽  
Accretion Rate ◽  
Be Stars ◽  
General Correlation ◽  
X Ray ◽  
Mass Accretion Rate ◽  
Debris Disk ◽  
Magnetic Nature

AbstractWe present the results of a new magnetic field survey of Herbig Ae/Be and A debris disk stars. They are used to determine whether magnetic field properties in these stars are correlated with the mass-accretion rate, disk inclinations, companion(s), Silicates, PAHs, or show a more general correlation with age and X-ray emission as expected for the decay of a remnant dynamo.

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